In this project, the role of CFTR in innate immunity, and its disruption by arsenic, will be examined in the zebrafish. There is evidence that the ATP-binding cassette (ABC) transporter protein, cystic fibrosis transmembrane conductance regulator (CFTR), is linked to the innate immune response and that mutations in CFTR result in increased susceptibility to lung infection in humans by Pseudomonas aeruginosa. Arsenic has been implicated in the perturbation of innate immune response and has been shown to inhibit the expression of CFTR in the killifish, Fundulus heteroclitus, however, a direct link between the action of this environmental toxicant and the disruption of CFTR function in innate immunity has not been established. In order to test these hypotheses, the SPECIFIC AIMS of this proposal are: 1. To investigate the relationship between exposure to the heavy metal toxicant, arsenic, and the activity of the innate immune response 2. To determine the relationship between CFTR expression and innate immune function in the zebrafish To examine the role of environmental toxicants in susceptibility to Pseudomonas infection in the zebrafish, the pathogen P. aeruginosa will be used to carry out infection studies and to determine if arsenic affects the innate immune response and alters patterns of resistance to infection. Respiratory burst assays will be performed to examine innate immune function in arsenic-treated fish. Zebrafish CFTR gene expression will be knocked down by a morpholino antisense oligonucleotide, and the resulting CFTR morphants, which will no longer bind P. aeruginosa IPS via CFTR, will subsequently be exposed to arsenic and evaluated for respiratory burst activity. In addition, RNA will be extracted from zebrafish embryos exposed to arsenic and the effect of treatment on CFTR expression will be determined by quantitative RT-PCR.